1. Field of the Invention
The present invention is directed to an arrangement for cooling an X-ray tube of the type having an electron beam deflector that is disposed externally of the evacuated housing of the X-ray tube.
2. Description of the Prior Art
X-ray tubes, particularly rotating anode X-ray tubes, are known which have an evacuated housing having a large space in which the rotating anode is mounted, and a chamber, projecting from the large space and communicating therewith through a narrowed neck region of the evacuated housing. The cathode is disposed in the chamber, and the electron beam emitted by the cathode proceeds through the neck region into the larger region, where it strikes a surface of the rotating anode at a focus, from which X-rays are generated.
In such a rotating anode X-ray tube, a U-shaped electron beam deflector, typically in the form of an electromagnetic yoke is disposed at the exterior of the evacuated housing, with the two legs of the yoke straddling the exterior of the neck region. These legs conventionally are formed of stacked laminations in order to reduce eddy current losses, and have a rectangular or square cross-section. The electron beam deflector has a coil that is supplied with current to generate a magnetic field that interacts with the electron beam passing through the interior of the neck region, so as to selectively deflect the electron beam, thereby adjusting the position of the focus on the anode.
A rotating anode X-ray tube of this type is described in U.S. Pat. No. 5,909,479.
In order to increase the effectiveness of the interaction of the electron beam deflector with the electron beam, it is desirable to place the electron beam deflector, or at least the aforementioned legs thereof, as close as possible to the electron beam, given the physical constraints imposed by the size of the neck region of the evacuated housing. This reduces the volume in which the magnetic field generated by the electron beam deflector must be present, and thereby allows a lower control current to be supplied to the coil. The neck region of the evacuated housing, however, is unavoidably disposed at a location that is subject to back-scattered electrons arising from the electron beam striking the anode. The neck region of the housing, therefore, is severely heated during operation of the X-ray tube. The more that the neck region is constricted in order to permit the electron beam deflector to be disposed closer to the electron beam, the higher the density of the back-scattered electrons in the neck region, and therefore the higher the heating that ensues.
It is conventional for an X-ray tube of any type to be disposed in a protective radiator housing, which is filled with a coolant, such as insulating oil, that is circulated to dissipate heat during operation of the X-ray tube. In a rotating anode X-ray tube of the type described above, wherein the evacuated housing has a narrowed neck region wherein heating is particularly severe, it is desirable to augment the normal flow of the fluid coolant in the radiator housing to direct a specific portion of the coolant toward and around the neck region. One such arrangement is known from U.S. Pat. No. 6,529,579 wherein a channel, in which liquid coolant flows, is arranged to surround the neck region, this channel being in fluid communication with a coolant circulator (pump). Not only does this known arrangement require rather complicated fabrication of the parts that form the coolant flow channel surrounding the neck region, but also this coolant flow channel must necessarily have a relatively small cross-section, because of the space confinements, and therefore the resistance to flow in this channel is high.